Duncan Coutts wrote:
This topic came up in #haskell this evening...
On Sun, 2008-08-24 at 16:12 -0700, Ashley Yakeley wrote:
1. Global mutable state. For instance, here's the count variable for Data.Unique rewritten:
uniqSource :: MVar Integer uniqSource <- newMVarTL 0
Isn't that much nicer? http://haskell.org/haskellwiki/Top_level_mutable_state
It's nicer syntax but it's still not true. There's still no such thing as a global variable. There's always a scope.
In this case what scope are we looking for? Process scope? Only one instance of ïğżuniqSource per process?
It is actually process scope, I believe. But it's one instance of "base-3.0.2.0:Data.Unique.uniqSource" per process: we don't care if there's also a "base-4.0:Data.Unique.uniqSource". The reason we don't care in this case is that base-3.0.2.0:Data.Unique.Unique and base-4.0:Data.Unique.Unique are different types, so they can't collide. These are different names in the same scope. The scope I'm interested in is "Main.main" scope, i.e., the initialiser should be run no more than once per run of "main". -- Ashley Yakeley